This invention pertains to thin-walled composite longitudinal structural members; particularly to composite beam or bar structures subject to global vibrations that create fluctuating extensional stresses in the walls.
Vibration of machines and structures can be undesirable for reasons of comfort, controllability, noise, or susceptibility to fatigue damage.
Add-on vibration damping treatments, including both free-layer and constrained-layer types, are commonly used to dissipate vibrations in structures fabricated from metallic and composite materials. Although these add-on treatments can attain high damping performance in certain instances, there are disadvantages in their use in that they add weight, create obstructions, and are vulnerable to damage by mechanical and environmental agents. They also tend to achieve desired performance over limited temperature ranges due to temperature sensitivity of the available viscoelastic materials.
Most of the existing applications of add-on damping treatments have been to control local bending modes of vibration such as plate bending modes in flat panels and shell bending modes in cylindrical sections; however, there are also needs for the damping of long-wavelength global modes of vibration including bending, torsional, and column modes.
In contrast to the more commonly treated local bending modes, the vibratory stresses accompanying the global modes are in-plane extensional stresses that are nearly uniform through the thickness of the wall. Add-on damping treatments have been used successfully to damp global modes in a few instances.
The problem to be solved then, is to overcome the disadvantages of add-on damping treatments particularly for the damping of long-wavelength global modes of vibrations while obtaining highly damped, lightweight construction of longitudinal members such as beam or bar structures.